In the fabrication of integrated circuits, photolithographic and projection printing techniques are used. A reticle or mask is used to transfer a desired image onto the silicon wafer. In the past the mask or reticle has been held with reticle frames to facilitate alignment and handling. The prior art reticle frames consists of rectangular frames having lapped pads spaced around the periphery. The lapped pads act as a reference point to establish a flat plane for holding the reticle. Three pads re typically used to define a single plane. Although the pads accurately define a reference plane they introduce undesirable stresses in the reticle which cause distortions.
The transverse positioning of the reticle within the plane established by the reticle frame and pads is necessary. In the prior art the two transverse adjustments are accomplished by a number of adjusting screws extending through the periphery of the frame. If the pads positioned along the periphery of the rectangular frame are considered to establish a plane perpendicular to the Z axis in a rectangular coordinate system then the adjusting screws would adjust the reticle along the X and Y axes relative to the frame. On the side of the reticle frame opposite the adjusting screws the transverse motions of the reticle are compensated for by plungers extending through the reticle frame. The plungers consist of rigid metal sleeves having spring loaded tips. While the adjusting screws and plungers provide accurate aligning of the reticle within the frame, undesirable bending moments and stresses develop in the reticle. This results in the reticle becoming slightly distorted. These distortions reduce the image quality reproducable on the silicon wafer. While the prior art devices perform adequately for most integrated circuit fabrication, the continuing quest for reduced size and higher density integrated circuits requiring much greater resolutions necessitated a new and innovated approach to the holding and aligning of a reticle.